Creation of a new LSM hook to check if a given configuration of vmflags,for a new memory allocation request, should be allowed or not.It's placed in "do_mmap", "do_brk_flags", "__install_special_mapping"and "setup_arg_pages".When loading an ELF, this hook is also used to determine what to dowith an RWE PT_GNU_STACK header. This allows LSM to force the loaderto silently ignore executable stack markings, which is useful a thing todo when trampoline emulation is available.